I have mixed feelings about this, since it got down to -14 one night late last year. I went ahead and put a heat lamp with a regular lamp in one of the hen houses. After a few nights, the hens started to use the unheated one! I even replaced the lamp with a red lamp (for reptiles), but my hens didn't come back - except to lay their eggs right under the lamp. Which was actually kind of nice since we haven't had a day above 40 here since November, and most days have been below 30. That meant I didn't have any frozen eggs. However, this may be something to think about - my hens, six now, have consistently laid between 28 to 30 eggs per week. They ARE young and breed-hardy (Aussies, Black Stars and NHR), but still compared with my other BTC pals, mine have outproduced everybody. Maybe its the light, I dunno.